Psychologists have classified these activities under three general expressions which we may call laws. They are, first, the law of Continuity; second, the law of Diversity of Purpose; and third, the law of Contrast.
The law of Continuity means that in the ethnic mental life there is a regulated course of growth or development; that each phase or condition is the logical result of previous phases or conditions.
The second law emphasises that the rate of growth depends chiefly on the diversity of aims which exists in the community. As they are multiplied, growth is the more rapid. This is analogous to that law of organic forms by which evolution is in proportion to variation.
The third law, that of Contrast, applies to the ethnic mind the curious fact in mental life that a prolonged devotion to one idea leads to a reaction in which the opposite of that idea becomes dominant. This is even more conspicuous in the history of progressive nations than in that of individuals. Upon this depends that periodicity in the lives of peoples which has so often been remarked by historians.
The above mentioned facts and laws demonstrate that there is a true unity of existence in the ethnic mind; that it has its own traits, forms, and processes of growth and decay, quite apart from those of the individual mind; that it is not to be studied by the methods of experimental psychology, but by methods drawn from the observation of its own modes of being; and that it is this abstraction, if you please, which is the prime factor in the fate of the group over which it rules.
But I must return again to the definition of the Group. It must not be said that I leave any obscurity in the connotation of that prominent word.
There may be—there always are—many forms of groups in the same community, and these by no means cover each other coterminously. Take many an American village, for example. There are the religious groups, Protestant and Catholic; the political parties, Republicans and Democrats, not at all of the same individuals as the former; and there may be the linguistic groups, German and American, different again from both the former; and the racial groups, whites and negroes.
Something similar to this is found on a large scale in every people, every nation; and the serious problem presents itself,—how are we, from these heterogeneous elements, to reach anything which we can properly call the common sentiment, the general mind of the mass?